The present invention relates to a connection structure for a display module and a printed substrate for connecting the display module, in which a display panel is connected with a semiconductor device formed by bonding and mounting a semiconductor chip on a flexible wiring substrate, to the printed substrate; the semiconductor device and the display module used in the connection structure; and an electronic component formed by connecting the display module with the printed substrate by means of the connection structure. More specifically, the connection structure of the present invention is appropriate for use in electronic devices requiring high-density wiring, such as a cellular phone or a pager unit.
Conventionally, in electronic devices such as a cellular phone and a pager unit, a so-called COF (Chip On Film) type semiconductor device, in which a semiconductor chip is bonded and mounted on a flexible wiring substrate, is widely used. On the other hand, a so-called TCP type (Tape Carrier Package), semiconductor device called, in which semiconductor chips are continuously connected on a flexible wiring substrate, is also used in many applications.
The difference between the COF and the TCP lies in a bonded section between an electrode on the semiconductor chip and an electrode on the flexible wiring substrate.
In the TCP, penetrating holes for mounting semiconductor chips are provided beforehand on a tape carrier material, which is a base substance of a flexible wiring substrate. Then, to each of the penetrating holes, a tip portion of a wiring pattern, called an inner lead, is projected like a cantilever, and the inner lead and an electrode of the semiconductor chip are joined.
On the other hand, in the COF, a penetrating hole is not provided on a tape carrier material in a section bonded with a semiconductor chip. That is, in the COF, a wiring pattern in the section bonded with an electrode of the semiconductor chip is backed with the tape carrier material.
When equipped with a liquid crystal driver IC as a semiconductor chip, the COF or the TCP constitutes a liquid crystal driver which drives a liquid crystal panel. Then, the liquid crystal driver and the liquid crystal panel constitute a liquid crystal module, which is provided as a display section in electronic devices such as a cellular phone.
FIG. 10 shows a case in which a COF is used as a liquid crystal driver for driving a liquid crystal panel which constitutes a display section of a cellular phone. In FIG. 10, a COF 32, which constitutes a liquid crystal driver when a semiconductor chip 31 is provided as a liquid crystal driver IC, is connected with a liquid crystal panel 33 so as to form a liquid crystal module 34. The liquid crystal module 34 is attached to a printed substrate 35 which forms an electronic circuit. Here, the COF 32 of the liquid crystal module 34 and the printed substrate 35 are electrically connected via a connector 36.
Conventionally, when connecting a COF (or TCP) of such a liquid crystal module and a printed substrate, a connecting method via a connecter, as mentioned above, and a connecting method using solder are widely used.
Meanwhile, when manufacturing an electronic device using such a liquid crystal module, especially that manufactured in large quantity such as a cellular phone, the following requirements should be satisfied in a process for attaching a liquid crystal module to a printed substrate (a connection process).
(1) Since a product test is conducted after attaching a liquid crystal module to a printed substrate, it should be designed that the liquid crystal module can be easily detached from the printed substrate.
(2) The connection of the liquid crystal module and the printed substrate can be easily automated, without recourse to manual connection.
(3) High reliability should be ensured in the connection of the liquid crystal module and the printed substrate.
However, in the foregoing method using solder to connect a COF of a liquid crystal module with a printed substrate, it is difficult to detach the COF from the printed substrate once they are connected. Therefore, the above requirement (1) cannot be satisfied.
Besides, in the method for connecting the COF of the liquid crystal module with a printed substrate using a connector, as shown in FIG. 10, a terminal section formed at one end of the COF 32 is inserted into the connector 36 for connection. However, since a flexible wiring substrate 32a, which is a base substance of the COF 32, is a soft film, it is difficult to automate the connection and thus manual connection is required. Therefore, the above requirement (2) cannot be satisfied.
Further, when using the connector 36, an actuator is required for pressing the terminal section of the COF 32, resulting in an increase in the number of components required. Besides, due to the adoption of the actuator, the total height of the connection structure on the printed substrate 35 is increased, which is disadvantageous for thin mounting structure.
To solve such problems, Japanese Unexamined Patent Publication No. 9-22760/1997 (Tokukaihei 9-22760, published on Jan. 21, 1997) discloses a method for connecting a liquid crystal module and a printed substrate which allows easy detachment and easy connection process automation. According to the publication, a snap-on method using pawls is adopted.
In this method, as shown in FIG. 11, engaged holes 44 are provided on a COF 42 of a liquid crystal module 41, near a connection pad 43 for establishing electrical connection with a printed substrate 45. On the printed substrate 45, in a section for fixing the liquid crystal module 41 is mounted a holding base 46, which is provided with a contact 47 corresponding to the connection pad 43 and holding members (pawls) 48 corresponding to the engaged holes 44. By snapping the COF 42 of the liquid crystal module 41 on the printed substrate 45, the corresponding engaged holes 44 and the holding members 48 are engaged so as to fix the COF 42 on the printed substrate 45.
At the same time, the connection pad 43 on the COF 42 and the contact 47 on the printed substrate 45 come into contact, and the connection pad 43 and the contact 47 are electrically connected.
In such a structure, by pressing the COF 42 onto the printed substrate 45 from one direction, the holding members 48 are snapped into the engaged holes 44. At the same time, the connection pad 43 on the COF 42 and the contact 47 on the printed substrate 45 are electrically connected. Therefore, the connecting process can be easily automated.
Meanwhile, such a snap-on method requires design ideas ensuring that the connection pad 43 on the COF 42 and the contact 47 on the printed substrate 45 are connected at the same time when the COF 42 is snapped on the printed substrate 45.
Because, for example, if the contact 47 on the printed substrate 45 is formed in a plane shape, in the same way as the connection pad 43 on the COF 42, the connection pad 43 and the contact 47 are difficult to make contact with each other just by snapping the COF 42 on the printed substrate 45, failing to obtain highly reliable connection. Especially, when the COF 42 is provided with components, the components might obstruct the contact between the connection pad 43 and the contact 47.
In response, in the foregoing publication, the contact 47 provided on the printed substrate 45 is formed as a conductive protruding electrode in a folded shape, and it is structured that the COF 42 is snapped on the printed substrate 45, pressing the contact 47 from above with the plane connection pad 43 on the COF 42.
However, the structure of the foregoing publication has problems as follows.
1) Space for placing the holding base 46 integrated with the holding members 48 and the contact 47 is required on the printed substrate 45, limiting the mounting area allocated for other components mounted on the printed substrate 45.
2) As for the placement of a liquid crystal panel on the printed substrate 45, the liquid crystal panel can be placed in an area except the snap-on section including the holding base 46, or placed above the snap-on section after the COF 42 is snapped on the printed substrate 45 and then folded.
However, in the former case, the liquid crystal module 41 occupies a large area on the printed substrate 45. Therefore, it is difficult to adopt the former case to an electronic device such as a cellular phone which requires to mount many components on predetermined space on the printed substrate 45.
In the latter case, the COF 42 is folded after snapped on the printed substrate 45 so as to fix a liquid crystal panel. Therefore, single-step mounting, that is, connecting the liquid crystal module 41 and the printed substrate 45 mechanically and electrically in a single step, cannot be performed.
Furthermore, in the latter case, the total thickness from a substrate surface of the printed substrate 45 to a display surface of the liquid crystal panel is increased by the thickness of the holding members 48 projecting from the COF 42, which is disadvantageous for thin mounting structure.
It is therefore the object of the present invention to provide a connection structure for connecting a display module and a printed substrate, by which mechanical and electrical connection between the display module and the printed substrate can be easily established, no limitations are set on the mounting area for other components mounted on the printed substrate, and the total thickness from the printed substrate to the display module can be decreased.
To achieve the foregoing object, a connection structure for a display module and a printed substrate of the present invention is for connecting a display module to a printed substrate, the display module including a display panel connected with a semiconductor device having a semiconductor chip mounted on a flexible wiring substrate, and is characterized in that:
the display module is fixed to a housing member in a folded state with respective rear surfaces of the semiconductor device and the display panel facing each other;
a protruding electrode is formed on the semiconductor device;
the display module is fixed to the printed substrate by means of a holding member (holding strip) attached to the housing member, the holding member supporting the printed substrate in engagement therewith; and
the protruding electrode formed on the semiconductor device is in contact with a connection terminal provided on the printed substrate corresponding to the protruding electrode.
According to this structure, the display module which is fixed (held) by the housing member in a folded state is pressed onto the printed substrate from above and snapped on the printed substrate. That is, with this structure, the holding member formed on the housing member engages the printed substrate and fixes the display module to the printed substrate. At the same time, the protruding electrode on the display module comes into contact with the connection terminal of the printed substrate for conduction. Consequently, the display module and the printed substrate can be mechanically and electrically connected in a single step.
Compared with the structure shown in FIG. 11 in which the holding base 46 integrated with the holding members 48 and the contact 47 is placed on the printed substrate 45, in the foregoing structure, there is no need to place a member for fixing the display module on the printed substrate. Therefore, only a contact is required to be provided on the printed substrate so as to come into contact with the protruding electrode on the semiconductor device.
Consequently, since no limitations are set on the mounting area allocated for other components mounted on the printed substrate, the foregoing structure is appropriate for use in electronic devices requiring high-density wiring, such as a cellular phone.
In addition, in the structure shown in FIG. 11, when the liquid crystal panel as the display panel is placed above a connected section connected by the holding members 48, the total thickness from a substrate surface of the printed substrate 45 to a display surface of the liquid crystal panel is increased by the thickness of the holding members 48 projecting from the COF 42. However, in the foregoing structure of the present invention, the total thickness from a substrate surface of the printed substrate to a display surface of the liquid crystal panel can be decreased by the thickness of the holding members, which is advantageous for thin mounting structure.
As for the protruding electrode formed on the foregoing semiconductor device, it is preferable to use a metal pin electrode terminal or a metal spring electrode terminal.
When the protruding electrode is a metal pin electrode terminal, a through hole electrode or a convex electrode is used as a connection terminal of the printed substrate so as to ensure the contact between the both terminals.
When the protruding electrode is a metal spring electrode terminal, even if the attachment height of the display module and the printed substrate varies in some degree, the elasticity of the spring permits the contact between the protruding electrode and the connection terminal of the printed substrate at all times. Therefore, stable conduction between the semiconductor device and the printed substrate can be always obtained.
In the connection structure of the present invention, the display module is attached in a folded state. Thus, it is preferable that the base substance of the flexible wiring substrate of the semiconductor device is made of a polyimide resin material with the thickness of 5 to 75 xcexcm, in consideration of bendability and easiness on handling.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.